You Can’t Have the Keys to the Mercedes: Understanding Alcohol Impairment

The study utilized a circular track approximately 1.5 miles long. Each test drive lasted about 15 minutes. To best simulate real-world conditions where alcohol-impaired collisions frequently occur, researchers conducted the trials at night and during winter. Testing was immediately halted during snowfall or icy conditions to ensure safety. Participants operated a specially instrumented Mercedes W124 300D, a vehicle equipped with technology to meticulously track eye movements and driver responses. They were instructed to maintain a steady speed of 45 km/h (27 mph) throughout the course.

To truly gauge the real-time effects of alcohol impairment, researchers engineered a surprise traffic situation in the final 30-60 seconds of the drive. A horn, triggered by a photoelectric beam, signalled the start of this sequence designed to mimic the unpredictability of real highways. The events unfolded as follows:

• A pedestrian crossed the track at a safe distance, entered a parked car, and turned on its headlights.
• A bicyclist with a light appeared on the left side of the road.
• A Volkswagen car approached from the opposite direction.
• The route passed a junction with three traffic signs (requiring no driver action).
• Two additional pedestrians walked on the left side of the track.
• A grey foam obstacle (3 feet x 1.5 feet x 1.5 feet) suddenly appeared, forcing the driver to take evasive action.

This complex scenario, centred around the “Versuchsfahzeug” or test vehicle, was crucial for measuring driver performance under duress.

The study involved 23 sober subjects and 25 who had consumed alcohol. The drinking group consumed their beverage of choice—beer, wine, vodka, or rum—resulting in a mean Blood Alcohol Concentration (BAC) of approximately 0.070 g/100mL (ranging from 0.054 to 0.092 g/100mL) at the start of the drive.

When reacting to the final grey foam barrier, the data was telling. The table of results clearly showed that drivers experiencing alcohol impairment had slower reaction times and a higher rate of both collisions and near misses compared to their sober counterparts.

Furthermore, this alcohol impairment affected cognitive recall; drinking drivers remembered significantly fewer details (3.7 items on average) of the surprise scenario than sober drivers (5.9 items).

Miraculously, the only damage recorded was to the Mercedes’ front spoiler, caused by a drinking driver who veered onto an icy patch.

The study’s conclusions are stark. Even at the low speed of 45 km/h, a definitive impairment of driving ability was observed in subjects with BACs below the common 0.08 g/100mL legal limit. This alcohol impairment was undeniable. The authors noted their findings align with the seminal Borkenstein Grand Rapids Study, which also confirmed that driving ability is compromised at levels under 0.08 g/100mL.

This research underscores a critical truth: alcohol impairment begins long before one reaches the legal limit. The findings from behind the wheel of that instrumented Mercedes are a powerful reminder of the risks associated with drinking and driving.

References
Wigmore on Alcohol: Courtroom Alcohol Toxicology for the Medicolegal Professional, Chapter 5.03 Closed-Course Driving Studies, Irwin Law, Toronto, 511pp, 2011.

For further reading on alcohol impairment and forensic toxicology, explore the expertise available at Wigmore on Alcohol.

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*All the references cited may be found in WOA 2e in the appropriate section according to the number.”